PT915917E - PROCESS FOR THE DECOMPOSITION OF A POLYMER IN ITS MONOMER OR MONOMEROS - Google Patents

Description

84 596

ΕΡ Ο 915 917 / EN

A process for the decomposition of a polymer into its monomer or monomers.

BACKGROUND OF THE INVENTION

This invention relates to a process for the decomposition of a polymer which is capable of undergoing thermal depolymerization for its monomer or monomers and for the recovery of at least one of the monomers which can be recycled to a process of polymerization. The conventional decomposition or depolymerization process for the depolymerization of poly (methyl methacrylate) (PMMA) waste makes use of a lead bath reactor. The PMMA residues are ground into small pieces (1 to 5 cm in diameter) and decomposed on the surface of a lead-melt bath. The melt lead is maintained at 520 to 550 ° C by means of a diesel burner operating at about 900 ° C. In the reactor, depolymerisation occurs by producing a gaseous product which is the monomer (methyl methacrylate) ("MMA"), which is condensed in a condenser, with a solid or gray residue remaining on the surface of the lead bath. The residue consists mainly of carbonaceous material, lead (40-60% m / m Pb) and inorganic residues of pigments and additives. The crude monomer (approximately 85%) of MMA) can then be purified as follows. The monomer is washed in a 9% caustic solution (containing 40 ppm copper sulfate heptahydrate CuSO 4 .7H 2 O), which removes any traces of lead. Wash liquids (containing approximately 12 ppm lead) are treated and discharged to a sludge deposition tank, but represent a potential environmental hazard. The final purification step is a vacuum distillation at 65 ° C to remove any heavy organic impurities. This type of depolymerization reactor can be operated to produce refined monomer having an average purity of 99.3% and a yield of 85%.

This type of depolymerization reactor has numerous disadvantages. The most significant drawback of the lead bath reactor is the environmental and safety hazards associated with lead. Another disadvantage of the reactor is that it has to be operated on a non-continuous basis. Generally, the reactor is shut down approximately after five days of operation due to surface fouling caused by the residue, which inhibits the transfer of heat from lead to PMMA. Cooling and cleaning may result in a one-day or two-day shutdown. A further disadvantage is that the lead containing the residue is generated as a waste. Lead has to be

84 596 ΕΡ0915 917 / ΡΤ 2 recovered from the residue, which then needs to be deposited in an environmentally suitable manner. The lead bath has subsequently to be reheated to the operating temperature. Thus, the process is energetically very ineffective.

In an article titled "Polymethyl Methacrylate Binder Removal from an Alumina Compact: Microwave versus Conventional Heating" in Mat. Res. Soc. Symp. Proc., Vol. 269, 1992, Moore et al., It is reported that compressed samples of alumina and methyl polymethacrylate were heated in a 2450MHz microwave oven by conventional heating in an electric fan. Various heating schemes were used to effect the removal of the polymeric binder by thermal decomposition. Dielectric properties, porosity and other physical properties have been investigated to better understand the binder removal process in a microwave field. The results of the study highlighted the amount of carbon residues remaining in the mass. In this paper it is reported that PMMA decomposes into monomer, water, benzene and other components. These components are then further broken down into hydrocarbons between 500 ° C and 1000 ° C. In other words, the PMMA is completely decomposed into hydrocarbons.

In an article titled "Microwave reactions of polyethylene terephtalate" in Polym. Mater. Know. Eng., 71, 531-2, 1994, by Gilmer et al., It is described that a vitrified reactor was designed for the microwave cavity to allow conventional chemical reactions to be performed without focused microwave heating. When using this assembly for reactions concerning the synthesis and depolymerization of polyethylene terephthalate (PET), the monomers for PET are generally not good microwave heaters (absorbers), with the possible exception of ethylene glycol (EG ). In the depolymerization of PET by EG and in the reaction of EG with methyl di-terephthalate to form bis (hydroxyethyl terephthalate) and methanol (MeOH), the same reaction rates were obtained using either thermal or microwave heating.

In other words, this paper generally describes the depolymerization of PET, in a solvent, i.e. EG.

Thus, there is a need for a new process for the decomposition of a polymer into its monomer or monomers, which makes use of an economical, safe and environmentally acceptable thermal decomposition pathway that eliminates the use of lead, and which results in a smaller quantity of "ashes" or "residues" and that is free of lead contamination. 3 84 596

ΕΡ Ο 915 917 / EN

SUMMARY OF THE INVENTION

According to the invention there is provided a process for the decomposition of a polymer which is capable of undergoing thermal decomposition in its monomer or monomers, the polymer being selected from the group consisting of poly (methyl methacrylate), polytetrafluoroethylene, polystyrene, poly ethylene), poly (Î ± -methylstyrene) and polyisobutylene, and to recover at least one of the monomers which comprises the steps of: (i) subjecting the polymer to a partially melted or molten solid form of a microwave heating for a period of time and at a temperature sufficient to decompose the polymer to produce the monomer or monomers in a gaseous, liquid or solid form without substantial decomposition of the monomer or monomers; and (ii) recovering at least one of the monomers or monomer. The polymer may be any suitable polymeric material which is capable of undergoing thermal decomposition into its corresponding monomer or monomers in reasonable yields and which is selected from the list previously provided. The polymer to be decomposed may be present as a single polymer, or in a mixture of two or more polymers. In the latter case, both or all of the polymers may be as listed above, or a polymer may be such as those listed above, and the other polymer or polymers may be different polymers, which may or may not decompose into their monomer or monomers . The process of the invention is of particular application to poly (methyl methacrylate), which undergoes a thermal depolymerization in methyl methacrylate, in up to 99% yield of the monomer. The process of the invention may include the following steps: (iii) when two or more monomers are recovered in step (ii), separation of the monomers from one another; (iv) when the monomer or monomers are in the gaseous form, condensation of the monomer or monomers; and

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(Ν) purification of the condensed monomer or monomers.

Thereafter, the monomer or monomers may, for example, be recycled to a polymerization process of the monomer or monomers to produce the polymer, or other polymers, or may be used to make other products.

Prior to step (i), the polymer may be preheated to a suitable temperature. The heating may be effected in any conventional manner.

In step (i), the polymer can be mixed with a microwave absorber or susceptibilizer, i.e. a material with a high dielectric loss factor. Examples of absorbers or microwave susceptibilizers are the coal powder (carbon black, fumed powder, soot); FREQUON B20, which is a fine white inorganic powder; M (03ZOxR) n wherein M = metal, Z = molecular weight group V atoms > 30, x = 0.1, R = H or organic radical, n = 1.2, for example Zr (03PCH2CH2SH); high loss ceramics, such as silicon carbide (SiC); ferrites; most electro-ceramics (e.g. barium titanate, BaTiO3); and materials based on alkali metal oxides (e.g., sodium oxide). The use of a microwave absorber or susceptibilizer may increase the decomposition process in polymers that by themselves do not interact or interact only weakly with microwaves (such as non-polar materials). Step (i) may be carried out under an inert atmosphere, for example, an atmosphere of nitrogen.

In step (i), microwave heating can be performed in a mono-mode, multi-mode or non-resonant cavity of a microwave reactor, at any suitable microwave frequency, and preferably at 2.45 GHz or 915 MHz, which are industrial frequencies. The process of the invention may be carried out on a continuous or discontinuous basis.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional diagrammatic view of a laboratory scale mono-mode microwave device for use in the method of the invention; Figure 2 is an expanded view of a portion of the mono-mode cavity of the device of Figure 1;

Figure 59 is a cross-sectional diagrammatic view of a modification of the mono-mode cavity of the device of Figure 1; Figure 4 is a cross-sectional diagrammatic view of a multi-mode laboratory microwave device for use in the method of the invention; Figure 5 (a) is a diagrammatic view on a bench scale of a mono-mode microwave reactor and the device for use in the process of the invention; Figure 5 (b) is a diagrammatic view of a variable source of microwave energy for use with the reactor of Figure 5 (a); and Figure 6 is a diagrammatic view of a non-resonant microwave multi-purpose reactor (± 1000 ml) and the device for use in the method of the invention.

Description of the Embodiments The crux of the invention is a process for the decomposition of a polymer which is capable of undergoing thermal depolymerization in its monomer or monomers, the polymer being selected from the group consisting of poly (methyl methacrylate), polytetrafluoroethylene, polystyrene , poly (Î ± -methylstyrene) and polyisobutylene, and to recover at least one of the monomers, which comprises the steps of: (i) subjecting the polymer to a solid, gel form, partially melted or melted at a microwave heating for a period of time and at a temperature sufficient to decompose the polymer to produce the monomer or monomers in a gaseous, liquid or solid form without substantial decomposition of the monomer or monomers; and (ii) recovering at least one of the monomers or monomer.

As the purpose of the invention is to recover at least one of the monomers, the microwave heating must be such that the monomer to be recovered is not substantially decomposed. Thus, the phrase "without substantial decomposition of the monomer or monomers" is to be interpreted in this way.

It should be noted that the polymer is subjected to microwaves in a solid, gel, partially molten or molten form. In other words, step (i) is carried out in the absence of

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A solvent or solvents for the polymer.

By "gel" is meant a system containing a range of products from the monomer to the polymer, i.e. a partially polymerized blend. The system does not contain solvent for the polymer. The process of the invention is particularly applicable to polymers selected from the group consisting of poly (methyl methacrylate), polytetrafluoroethylene, polystyrene, poly (α-methylstyrene) and polyisobutylene, ie excluding polyethylene terephthalate, since the degradation of this polymer to recover both monomers, ethylene glycol and terephthalic acid, involves a hydrolysis reaction, which requires the presence of a suitable solvent such as ethylene glycol or other hydroxide-containing species, for example methanol. In the process of this invention, only terephthalic acid can be recovered in the absence of a solvent. The process of the invention is more specifically for application to poly (methyl methacrylate).

As noted above, the polymer to be decomposed may be present as a single polymer or in admixture of two or more polymers. In the latter case, both or all of the polymers may be as listed above, or a polymer may be as listed above, and the other polymer or polymers may be different polymers which may or may not decompose into their monomer or monomers.

Accordingly, the process may be selectively used to decompose and recover the monomer of a polymer substance, or to decompose and recover two or more monomers sequentially, from a copolymer or a physical blend of various polymers, wherein the and the dielectric loss factors are conveniently different to allow this. In the process, the decomposition temperature is controlled so as to prevent a substantial degradation of the monomer or monomers into hydrocarbons or other undesirable carbonaceous materials.

As stated, the process of the invention is of particular application for the depolymerization of acrylic resins and polymers, more particularly poly (methyl methacrylate), or copolymers of physical blends of poly (methyl methacrylate) with other polymeric substances. The polymer may be treated in a gel form, partially melted or fused, or 7 84 596

In solid form in the form of small pieces, for example having a diameter of 0.1 to 5 cm, or as a powder. The process of the invention is of particular application for the depolymerization of acrylic products, obtained either by casting or by extrusion, and high impact acrylic products, which may contain other recyclable (e.g. polystyrene) or non-recyclable components. It is also used in the recycling of PMMA residues and acrylic powder products, also known as filings, obtained from the cutting of PMMA and acrylic products, and PMMA gel (partially polymerized PMMA / MMA blend).

In step (i) the polymer can be mixed with a microwave absorber or susceptibilizer, i.e. a material with a high dielectric loss factor. An example of a suitable microwave absorber or susceptibilizer is carbon black. Other examples are given above. Carbon black is a very efficient microwave absorber, which heats up in seconds, increasing the decomposition of the polymer. Thermal energy is transferred from the carbon black to the polymer, which results in rapid decomposition. The mass percentage of the carbon black added may be from 0.5 to 50%, preferably from 0.5 to 5% by weight of the polymer. The carbon black is unaffected in the inert atmosphere and can thus be recycled, provided the residual inorganic pigments do not interfere with the process.

However, it is not always necessary to use an absorber or a susceptibilizer. By optimizing the cavity design (geometry and dimensions), the conjugation with the material to be heated is maximized, reducing the need for a susceptibilizer. For example, in the case of PMMA, after optimization of the reactor design, no microwave absorber or susceptibility is required, since PMMA is efficiently conjugated with microwave energy. Step (i) may be carried out under an inert atmosphere, e.g. an atmosphere of nitrogen. The nitrogen atmosphere is used to remove the gaseous product from the reaction zone and to prevent the ignition of hot volatile organic vapors in the case where the monomer is released as a flammable vapor or liquid. Nitrogen also serves to prevent ignition of carbon, when it is used as a microwave susceptibilizer.

Furthermore, in order to prevent condensation of the gaseous products on the walls of the microwave reactor, it is possible to heat the walls of the microwave reactor by conventional means.

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ΕΡ Ο 915 917 / EN 8

Prior to step (i), the polymer may be preheated to a suitable temperature, the heat being produced by any conventional means. The reason for this is that it has been found that the microwave absorption efficiency of some polymers, such as PMMA, increases with increasing temperature. This property can be used to improve the overall efficiency of the process of the invention. Thus, the polymer can be conventionally preheated in order to improve the microwave absorption efficiency and then, at elevated temperature, the polymer is irradiated with microwave energy. The advantages of preheating include the fact that the microwave absorption efficiency can be improved by more efficient conjugation of the energy with the polymers at an elevated temperature, and the overall process energy cost can be reduced by hybrid heating , since microwave heating is only used in the most effective decomposition zone (temperature).

When the polymer is PMMA, the PMMA can be preheated to a temperature of from 80 ° C to 150 ° C inclusive. However, with a suitable design microwave device, PMMA is most effectively conjugated to microwave energy, and preheating is not required. Microwave heating may be performed in a mono-mode, multi-mode or non-resonant cavity of a microwave device having any suitable microwave frequency determined by measurements of dielectric properties, and more preferably with an industrial frequency such as 2 , 45 GHz or 915 MHz. The microwave radiation directly interacts with and heats the polymer, causing decomposition to take place. The microwave energy can be generated by a magnetron or klistrão, using electrical energy. The microwaves are generated in a microwave generator and transferred to a mono-mode, multi-mode or non-resonant cavity by means of a waveguide. The power requirements will depend upon the dielectric properties of the material under radiation at a particular frequency, the mass of the material, the feed rate and the efficiency of the system. The microwave device preferably allows fine tuning of the microwave radiation applied to the cavity to maximize the electrical field density in the polymer region, and thereby improve the depolymerization efficiency of the polymer.

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The process may be carried out on a discontinuous basis or on a continuous basis by continuously feeding the polymer into the microwave cavity and, in the case of a gaseous product, by removing the gaseous product from the reaction zone. The inert gas removed may pass either in co-current or countercurrent with respect to the passage of the polymer. The process may also be operated without a continuous withdrawal of the inert gas with a suitable design of the apparatus. The residence time of the polymer under microwave radiation will be determined so as to obtain the desired degree of decomposition of the polymer without substantial decomposition of the monomer that occurs and is also related to the type and mass of the polymer being decomposed with the dielectric properties of the polymer, the feed rate, the power utilized and the design efficiency of the system. As noted above, conventional preheating the polymer prior to microwave radiation reduces the required radiation time, since the efficiency of microwave absorption is improved.

Likewise, the use of a susceptibilizer reduces the required radiation time, which is again dependent on the foregoing factors, in addition to the ratio (m / m) of polymer to the susceptibilizer.

In general, it is desirable to limit the maximum temperature within the microwave device, so as to decompose the polymer into its monomers / monomer, without further degradation of the monomers / monomer.

In the case of two polymers (i.e., a blend or copolymer), in the absence of a susceptibilizer, the upper temperature is strongly determined by the polymer with the highest dielectric loss factor, ie which absorbs or interacts more strongly with the microwave energy with a particular frequency. An example of this is the case of a mixture of PMMA and polystyrene, wherein the higher temperature is determined by PMMA, due to its greater interaction with microwave energy. In this case, the maximum decomposition temperature is higher than the typical temperature range for the decomposition of the second polymer (polystyrene). As long as this maximum temperature does not exceed the temperature at which further degradation of the monomer occurs from the decomposition of the second polymer (Π), both monomers of the polymers (I) and (Π) can be recovered simultaneously. However, if the maximum temperature does not exceed the degradation temperature of the second monomer, only the monomer of the first polymer (I) can be recovered. This is equally applicable to mixtures containing more than two polymers.

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In the case of two or more polymers (ie a blend or a copolymer), in the absence of a susceptibilizer, wherein the maximum or upper temperature defined by the polymer (I) with the highest dielectric loss factor is sufficiently below the (and subsequent polymers, III, IV, etc.), then it may be possible to selectively decompose the first polymer and recover the monomer from the polymer (I) selectively prior to the decomposition of the second polymer (II) ( and subsequent polymers ΙΠ, IV, etc.), and recovery of the monomer (monomers). Invariably, some decomposition of the second and subsequent polymers can occur concomitantly with that of the first, to varying degrees, if the temperature ranges of decomposition overlap with that of the first polymer. When the second polymer (Π) (and subsequent polymers ΙΠ, IV, etc.) does not interact or interact only weakly with microwaves, it may be necessary to add a suitable susceptibility material to the reactor after decomposition of the polymers , which interacts strongly with the microwaves so as to increase the temperature for further decomposition of the remaining polymers.

Generally, with the PMMA, the decomposition starts at about 300 ° C and is complete at about 400 ° C. Further heating above 400 ° C results in the undesirable formation of tars caused by the decomposition of the monomer into undesirable carbonaceous products.

Thus, it is essential to carefully control the temperature in the case of PMMA to avoid a substantial increase in temperature above 400 ° C. This is another reason for periodic removal of the inorganic pigment residues, which can further increase the energy of the microwaves by accumulation, leading to thermal leakage and substantial tinder formation of the product, and in reduced purity and recovery of the monomer.

In the case of polystyrene, the decomposition temperature range shall be limited to 230 to 400 ° C.

In the case of polyethylene terephthalate the range of decomposition temperatures shall be limited to 300 to 450 ° C.

In the case of polytetrafluoroethylene, the decomposition temperature range shall be limited to 450 to 550 ° C.

In the case of poly (Î ± -methylstyrene), the range of decomposition temperatures should be limited to 200 to 500Â ° C.

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ΕΡ Ο 915 917 / EN 11

In the case of polyisobutylene, the decomposition temperature range shall be limited to 300 to 400 ° C.

However, the above temperature limits, given as an indication, are defined for individual polymers and the upper temperature limits for blends will be naturally dependent on the composition of the polymer / copolymer blend, the gaseous atmosphere and the pressure at which the decomposition is conducted . In the presence of a susceptibilizer, temperature control is vital to prevent thermal leakage and to avoid substantial degradation of the monomer / monomers.

The products of step (i) are first the monomer or monomers in gaseous form and secondarily a small amount of residue, which mainly comprises inorganic pigments and gray (carbon) pigments. The residue can be periodically removed from the microwave reactor by a suitable design of the apparatus to prevent the entry of oxygen or air into the reaction zone, or leakage of microwave energy from the reactor.

In the case of polyethylene terephthalate, the terephthalic acid is recovered in a solid monomeric form from the microwave cavity itself.

After step (ii), which comprises recovering the monomer or gaseous monomers, the gaseous monomer or monomers may be subjected to one or more of the following steps.

When two or more monomers are recovered in gaseous or liquid form, the monomers may be separated from one another, for example by distillation. In the case of distillation the gaseous monomers are first condensed.

Accordingly, the monomer or monomers may be condensed by conventional means.

If necessary, the condensed monomer or monomers may be purified by conventional means before being recycled to a polymerization process, or before being used, in the manufacture of other products.

In the case of polyethylene terephthalate, the recovered solid terephthalic acid can be purified by conventional means.

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The invention also covers the use of a monomer produced by the process described above in a polymerization process of the monomer, optionally with one or more additional monomers, and optionally mixed with the virgin monomer, in a suitable ratio, to produce a polymer.

Also, the invention covers the use of the monomer produced by the process described above in the manufacture of other products.

For example, in the case of PMMA, the recovered MMA monomer can be used in the manufacture of plastic resins and acrylic fibers, impact modifiers and processing acids, emulsion polymers, mineral base sheets, polyesters, polymer concrete and methacrylate specialties such as methacrylate. butyl acrylate, stearyl methacrylate, decyl methacrylate and 2-ethylhexyl methacrylate.

In the case of polystyrene, the recovered styrene monomer can be used in the manufacture of acrylonitrile-butadiene-styrene (ABS) resins, styrene-acrylonitrile (SAN) resins, styrene-butadiene (S / B) copolymer latexes, resins unsaturated polyesters, elastomers and latexes of styrene-butadiene rubbers (SBR), styrenated phenols, styrene oxide and styrenated oils.

In the case of polyethylene terephthalate, recovered and purified terephthalic acid may be used in the manufacture of polyester films and fibers, solid poly (ethylene terephthalate) resin, terephthaloyl chloride, dioctyl terephthalate, polymers of liquid crystal, amorphous nylons, thermoplastic resins and dimethyl tetrachloroterephthalate, and as a raw material in the synthesis of fine organic chemistry. The invention will now be further described with reference to the accompanying drawings. Referring to Figures 1 and 2, there is shown a microwave-scale device 10 on a laboratory scale. The device 10 includes a microwave energy variation unit 12 of 6 kW with an operating frequency of 2.45 GHz. The power unit 12 is adjusted with the supplied power controllers 14 and reflected 16. The power unit 12 there is connected a waveguide 18 with a mono-mode cavity 20 located in an aperture in the waveguide 18, but designed to prevent any microwave leakage. In the microwave guide 18 a tuning adapter 22 is mounted to tune the microwave energy that is supplied to the cavity 20 and an insulator 24 to absorb the reflected energy. The microwave energy is transferred through the waveguide 18 into the mono-mode cavity 20 where they are absorbed by the polymer 26. A quartz tube 28 or any

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Another suitable microwave-transparent vessel holds the polymer 26 inside the microwave cavity 20. The tube 28 is mounted with gas seals 30 to allow efficient product recovery and an effective inert gas atmosphere. The inert gas is introduced at 32 and controlled through a calibrated flow meter 34. The gaseous monomer product is condensed into two liquid nitrogen traps 36 or other suitable equipment. The device 10 is placed in a smoke retention compartment 38 for safety reasons to remove any organic vapor which is not condensed by the liquid nitrogen traps 36.

Referring to Figure 3, reference 40 generally indicates a modification of the mono-mode cavity 20 depicted in Figures 1 and 2 which includes additional features necessary to tune the microwave cavity to maximize the conjugation of the microwave energy to the polymer to be irradiated. The mono-mode cavity 40 comprises an opening in a waveguide 42 designed to prevent microwave leakage. The waveguide 42 is connected to a variation microwave supplier 44 which is mounted with controllers of the supplied power 48 and reflected 46. The waveguide 42 is mounted with a short circuit device 50, an adjustable aperture 52 and tuning tunnels 54 used to tune the microwave energy supplied to the cavity 40. By adjusting the position of the wave in the waveguide 42, it is possible to minimize the reflected energy and maximize the conjugation of the microwave energy with the polymer to be irradiated.

Referring to Figure 4, there is shown a laboratory-scale microwave device 60 mounted with a multi-mode cavity 62. The device 60 includes a microwave energy variation unit 64 of 6 kW with an operating frequency of 2 , 45 GHz. The power unit 64 is adjusted with the supplied power controllers 68 and reflected 66. The power unit 64 is connected to a waveguide 70. The multi-mode cavity 62 comprises a stainless steel cavity designed to contain the microwave energy supplied by the power unit 64. In the microwave guide 70 a tuning adapter 72 is mounted to tune the microwave energy that is supplied to the cavity 62, and an insulator 74 to absorb the reflected energy and thereby protect the magnetron. The microwave energy is transferred through the waveguide 70 into the cavity 62 where it is absorbed by the polymer 76. The polymer 76 may be placed directly into the cavity 62. Altematively, the polymer is placed in a ceramic support within a microwave-transparent vessel 78, airtight. When the monomer is in gaseous form the product is removed out of the transparent vessel to the microwaves 78 and condensed out of the microwave cavity 62 through a gas outlet 80. The vessel 78 is constantly purged with an inert gas through an inlet

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The entire device is enclosed in a smoke trap compartment 84 for safety reasons.

Referring to Figure 5 (a), there is shown a countertop (1.5-2 kilograms per hour, semi-continuous) microwave device 90 mounted with a mono-mode cavity 92. The device 90 includes a microwave energy variation of 6 kW (Figure 5 (b)) with an operating frequency of 2.45 GHz. (On a industrial scale, a frequency of 915 MHz is more favorable). The power unit 94 is adjusted with the supplied power controllers 96 and reflected 98 as shown in Figure 5 (b). A waveguide 100 is connected to the power unit 94. The mono-mode cavity 92 comprises a cylindrical cavity 102 in stainless steel. The mono-mode cavity 92 is especially designed so as to maximize the electric field in the lower section of the reactor 92, and the cavity is specially tuned by creating a small aperture 104 in the center of the cavity wall, wherein the waveguide 100 makes contact with the wall. The dimensions of the aperture 104 are critical to maximize the conjugation of the energy in the cavity 92. In order to prevent substantial amounts of gaseous product from diffusing and condensing in the waveguide 100, which may cause fire, a quartz window 106 to the microwave energy) in the flange 108 with a collar and special seals in the section 110 of the waveguide 100 in contact with the reactor 92. This section 110 of the waveguide 100 has a jacket to allow cooling (water or other refrigerator). A nitrogen purge port 112 is placed between this section 110 and the wall of the cavity 102 to prevent condensation of gaseous product in the quartz window 106. As a precaution, in case the quartz window 106 is damaged, a second window system quartz / flange 114 is located further on waveguide 100 to protect the magnetron. The section of the waveguide between the quartz windows 106 and 114 is purged with nitrogen through the inlet 112.0 nitrogen gas exits at the outlet 116 and can be tested for the presence of monomer through a suitable gas-sensitive device (eg a tube of Dräger).

A polymer 118 is fed to a cavity 92 through a feeder 120. The feeder 120 is connected to a feeder tube 122, sealed between two valves 124 and 126. A nitrogen inlet 128 allows this tube 122 to be purged of the oxygen during The feeding. The operation involves opening the upper valve 124 at the same time as the lower valve 126 is closed, filling the tube 122 with polymer while purging with a flow of nitrogen (port 128), and then the upper valve 124 is closed. The lower valve 126 is then opened to allow the polymer to fall through the section 130, is heated with the heating tape, before falling into a through-flow reducer 132, purged with nitrogen through the inlet 134. The lower valve 126 is immediately closed after that, to

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Avoiding the diffusion of the gaseous product into the feed mechanism, which may cause adhesion and result in a blockage of the tube 122. The pass-through reducer 132 is designed with dimensions adequate to avoid loss of radiation energy from the cavity 92. The polymer 118 falls through the cavity 92, where it may be preheated (although this is not necessary in the case of some polymers, eg PMMA) prior to radiation with the microwave energy, by any conventional heating means, in this case a heating strip 136, set to a predetermined temperature. When the monomer is recovered in the gaseous form, the gaseous product obtained from the decomposition of the polymer exits the reactor 92 through the outlet 138 (of suitable dimensions so as not to allow loss of microwave from the cavity) and passes through a heated line to a cooled condenser 140 and suitably drawn prior to being collected in a suitable vessel 142 which may or may not be still cooled. Samples of the condensate collection vessel 142 may be drawn at a sampling point 144 to allow the purity and composition of the product to be determined periodically during the reaction. The gaseous purge nitrogen exiting the system through the collection / collection vessel 142 at the outlet 146 is continuously monitored by an oxygen analyzer for safety reasons.

For safety reasons, a pressure relief valve 148 and a pressure monitoring device 150 (eg manometer or pressure indicator) may be connected to the cavity 92 in the upper flange 152 of the cavity 92, provided that the dimensions are such that leakage occurs.

A thermocouple 154 is located in the gas outlet pipe 138 to monitor the temperature of the gaseous product prior to condensation. Another thermocouple 156 is located in the lower region of the cavity 92 (in the polymer region) to monitor the temperature during decomposition. The feed rate is controlled by monitoring the reflected energy 98 (see Figure 5 (b)) by matching the feed rate to the rate of decomposition in the well. The entire reactor 92 is isolated by encapsulating it with a suitable reagent material (insulation) such as Fibreffax ™ 158.

Referring to Figure 6, there is shown a 1000 ml multi-purpose microwave device mounted with a non-resonant cavity 160. The device includes a microwave energy variation unit of 6 kW, with an operating frequency of 2 , 45 GHz. The power unit is adjusted with the supplied and reflected power controllers. The power unit is connected to a waveguide 162. The waveguide 162 is mounted with a non-resonant cavity 160 and an adjustable short-circuit device 164. The

84 596 ΕΡ Ο 915 917 / ΡΤ 16 adjustable short-circuit device 164 is used to dynamically adjust the impedance matching as the load changes. To prevent diffusion of the degradation products in the waveguide 162 and the short circuit device 164, the cavity 160 is mounted at each end with a pair of waveguide quartz windows 166. Each quartz window 166 is sealed with specially designed flange fittings, with a special collar and seals. The nitrogen inlets 168 purge the oxygen cavity 160 and the waveguide section 162 between each pair of the waveguide windows 166, respectively. A methyl methacrylate Dräger tube 170 (or other suitable gas sensitive device in the case of other polymers) is connected to the nitrogen outlet in the waveguide section 162 between each pair of waveguide windows 166. The a quartz window 166 closer to the cavity 160 is indicated by a color change of the Dräger tube 170 (caused for example in the case of PMMA, by the presence of methyl methacrylate). The gaseous product obtained from the decomposition of the polymer exits the cavity through the outlet 172 (of suitable dimensions so as not to allow microwave leakage from the cavity) and passes through the condenser 174, before being collected in a suitable collection vessel 176 A gas pump 178 is connected to the collection vessel 176 to allow a sample of gas to be collected for analysis. The line between the cavity 160 and the condenser 174 is heated through a heating tape to prevent condensation of the monomer in the line to the condenser 174. A thermocouple 180 is located in the lower region of the cavity 160 to monitor the temperature during depolymerization. A thermocouple 182 is located in the gas outlet tube 172 for monitoring the temperature of the gaseous products prior to condensation.

For safety reasons, a pressure gauge 184 is connected to the nitrogen purge inlet line 168 to monitor the pressure and allow pressure relief if a blockage occurs downstream of the outlet point 172. And an oxygen meter is connected at the point to monitor the oxygen levels in the exhaust gases. The nitrogen regulators regulate the flow of nitrogen in the various nitrogen purge lines. The well is charged with approximately 700 ml of polymer, prior to mounting of the waveguide. The system is then purged with nitrogen and the polymer is then irradiated with microwaves, as the oxygen levels in the flue gases are less than 0.5%. An adjustable short-circuit device is adjusted during operation to minimize reflected energy. A sample of the top space gas is collected (e.g. from the space above the condensate) in a gas pump, once it is evident that condensation is occurring. The operation is stopped as soon as the measured temperatures in the gas outlet cavity and tubing begin to fall rapidly (an indication that the depolymerization has ceased) and no further condensate is produced (monitored by the condensate level in the collection vessel).

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ΕΡ Ο 915 917 / EN 17

This system (Figure 6) represents a multi-purpose microwave device for testing a range of different polymers and polymer blends. In the examples provided (non-resonant cavity), this system was used to demonstrate only the depolymerization principle and was not optimized for any particular polymer. Adequate fit of the cavity and optimization of conditions by those skilled in the art will allow for the maximum depolymerization of the polymer, and collection of the monomer / monomer to a particular polymer or polymer system. The invention will now be further illustrated by way of several examples, which were carried out in the aforementioned device.

All recoveries were calculated as the mass of condensed monomer as a percentage of the mass of depolymerized polymer. All yields were calculated as the mass of condensed monomer as a percentage of the total mass of the polymer added to the well.

Example 1 - Application of the process of the invention to PMMA

Example lta)

Decomposition of poly (methyl methacrylate) in the mono-mode cavity (laboratory scale)

A sample of poly (methyl methacrylate) powder (± 1 g) was irradiated in the mono-mode microwave cavity with 200 W of power supplied for 60 seconds (10% of the power was not absorbed by the material). The condensed product was analyzed for purity by quantitative gas chromatographic (GC) analysis which indicated 99% product purity. The mass loss of the polymer was 96% and the monomer yield was 86%.

Example lib

Decomposition of powdered poly (methyl methacrylate) in a mono mode cavity (laboratory scale)

A sample of powdered fused poly (methyl methacrylate) (<500 μm, 3.1 g) mixed with approximately 1% (w / w) charcoal powder (as microwave susceptor) was irradiated in the microwave cavity mono mode (Figure 1) with 1 kW of power supplied for 2 minutes. The mass of the residue in the cavity after irradiation has

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The loss was determined and the mass loss of the polymer was then calculated to be 97%. The gaseous product was analyzed by Gas Chromatography - Mass Spectrometry (GCMS) and found to contain predominantly MMA, with traces of styrene, indene, naphthalene, dimethyl terephthalate and dibutyl phthalate.

Example 1 (ci

Decomposition of poly (methyl methacrylate) into a mono-mode cavity (bench scale reactor)

A sample of poly (methyl methacrylate) (PMMA) (220 g) was charged into the microwave cavity (Figure 5). The microwave reactor was slowly heated (for 2.5 hours) to a maximum of 200 ° C using a heating tape wound around the cavity. This was done either for a thermal shock on the ceramic insert, or also for preheating the polymer to improve the conjugation of the microwaves to the material. The energy supplied was then increased slowly over a period of 10 minutes to a maximum of 4 kW. During the experiment a further 1647 g of PMMA was added to the reactor in small increments, while continuously irradiating (at 4 kW) over a period of 120 minutes. The energy supplied and reflected and the reaction time were not optimized during the experiment). There was a mass loss of 99.3%. An analysis of the residue in the cavity ("ash" or "slag") after irradiation has stopped using X-ray fluorescence showed the following "ash" or "slag" composition, which reflects the inorganic pigments and additives in PMMA original:

Ba (30%); Cd (0.6%); Sr (0.5%); Fe (0.5%); Cr (0.5%); Ti (16%); Ca (0.5%); K (&lt;0.5%); S (4%); AI (4%); O (28%). (Other elements (Ni, Zn, Se, Cu, Si, Nd, Sb) were less than 0.1%). (Note: During previous development work (prior to the design of the quartz window system), a high purity cylindrical alumina insert was used to line the interior of the stainless steel cavity. The narrow space between the stainless steel wall and the ceramic insert was sealed at each end using Teflon seals. The function of the ceramic insert (transparent to the microwaves at these temperatures) was to prevent diffusion of the monomer vapors into the waveguide and thereby serve to protect the magnetron. In view of the practical difficulties associated with this system, the improved design was developed with a quartz microwave window system as described in Figure 5, which was adopted in all subsequent work on the bench scale described herein.

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Example 1d)

Decomposition of poly (methyl methacrylate) into a mono-mode cavity (bench-scale reactor) with conventional preheating

During the prior experimental work (ie prior to optimization of the design), a series of experiments were carried out in which the initial polymer temperature (PMMA) ranged from 73 ° C (case 1) to 95.3 ° C (case 2 ), 134øC (case 3) and finally 192øC (case 4), and the sample was irradiated under the same supplied energy conditions (2 kW) for 40 minutes, with subsequent PMMA additions after approximately 10 minutes (50 g), 20 minutes (50 g) and 30 minutes (50 g), in each case. The following mass losses were recorded after the same total reaction time, demonstrating the beneficial effect of sample preheating &gt; 100 ° C.

Case 1 (73 ° C) 46.0% Case 2 (95.3 ° C) 41.9% Case 3 (134.3 ° C) 80.1% Case 4 (192 ° C) 81.9%

There appears to be a critical temperature (> 100 ° C), above which no increase in the initial mass loss rate is gained with increasing temperature. Similarly, preheating at any temperature below 95øC results in low initial mass losses, only about 40-45%.

During subsequent optimization of the reactor design and other process conditions, it was found that it was not necessary to preheat the PMMA. However, preheating may still have a beneficial effect on other polymers.

Example 1 (the

Decomposition of poly (methyl methacrylate) in the multi-mode cavity (laboratory scale)

A sample of poly (methyl methacrylate) particles (± 330 g) was irradiated in the multi-mode microwave cavity with 1600 W of power supplied for 23 minutes. The mass loss of the polymer was 98% and the purity of the product was 97%. (The supplied and reflected energy and the reaction time were not optimized).

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Example 1 (f)

Decomposition of poly (methyl methacrylate) molded into a mono-mode cavity (bench-scale reactor)

The walls of the microwave reactor were preheated to a maximum of 200 ° C using a heating tape wound around the cavity to prevent condensation of the monomer on the cavity walls. The reactor system was purged with nitrogen, and oxygen levels were monitored through an oxygen analyzer placed in the outlet to the collection vessel. The energy supplied was set at 1 kW and a sample of molded poly (methyl methacrylate) (130 g) was incrementally fed through a valve system into the microwave cavity for a period of about 2 minutes (Figure 5). During the experiment a further 5-6 kg of PMMA was added in small increments (in order to minimize reflected energy), while continuously irradiating (at 1 kW) for a period of 3.5-4 hours. The reaction temperature recorded during the depolymerization was in the range of 320 to 390øC. An average depolymerization rate of 1.4 kg / h was calculated. A total polymer mass loss of 98-99% was recorded. The average purity of the recovered methyl methacrylate monomer (MMA) was 95% (1% standard deviation), and the overall recovery of MMA and the yield in MMA were 93% (1% standard deviation) and 90% % (standard deviation of 0.5%), respectively. The true energy utilization in the cavity was calculated as 0.714 kWh / kg PMMA (without taking into account the electrical conversion efficiency of the source to the magnetron).

An analysis of the residue in the well after irradiation, using Nuclear Magnetic Resonance Spectrometry (NMR), showed the presence of PMMA (only) with a molecular weight of approximately 16,000.

Exemnlo lfgf

Decomposition of pigmented or stained poly (methyl methacrylate) in a mono-mode cavity (bench scale reactor)

Using procedures similar to those carried out in Example 1 (f), pigmented (1662 g) and stained (5053 g) samples of poly (methyl methacrylate) were depolymerized in separate experiments for periods of 1 hour and 3 hours, respectively. The reaction temperature recorded during the depolymerization was in the range of 330øC to 390øC. The mass losses, purity of the MMA produced (determined by GC analysis), the

I

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MMA recovery and MMA yield were as follows:

(%) MMA purity (%) MMA recovery (%) Yield in MMA (%) Pigmented PMMA 94 98.1 94 88 PMMA stained 98 94.3 93 91

EXAMPLE 1 (g)

Repolymerization of a monomer in its polymer

A sample of MMA, prepared by depolymerization of pigmented PMMA (as described in Example 1 (g) (1)), was distilled at atmospheric pressure. 700 g of the distillate were activated and gently heated for 30 minutes to produce a partially polymerized low viscosity gel (syrup). The gel was doped with various agents including a cleavage aid and a surge suppressor prior to repolymerisation to form a sheet having the dimensions 4 mm x 356 mm x 356 mm. The last sheet of PMMA (produced from 100% depolymerized PMMA) was tested for ease of cleaving from the molding mold, the edges and the color of the sheet, clarity, heat quality test and reduced viscosity . These results were found to be comparable to the results obtained for a typical commercially produced PMMA sheet.

Example 1 (h)

Decomposition of transparent poly (methyl methacrylate), obtained by molding into the non-resonant cavity

A sample of transparent, molded poly (methacrylate) particles obtained by molding (381 g) was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6) with 1 kW of energy supplied for 20 minutes. The temperature of the reaction recorded during the depolymerization was in the range of 360 ° C to 385 ° C. The mass of the residue in the well after irradiation was determined was determined and the loss of mass of the polymer was then calculated to be 58%. The purity of the MMA product was determined by GC analysis to be 98.7%, resulting in an overall recovery of MMA and an MMA yield of 80% and 46%, respectively.

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Example 1 (Τ)

Decomposition of transparent poly (methyl methacrylate), obtained by extrusion in the non-resonant cavity

A sample of transparent poly (methyl methacrylate) particles obtained by molding (500 g) was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6) with 1 kW of power supplied for 36 minutes. The reaction temperature recorded during the depolymerization was in the range of 300 ° C to 400 ° C. A sample of the top gas was withdrawn after 14 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain: carbon dioxide; 2-methyl-1-propene; acrylate and MMA. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 86%. The condensate was analyzed by GC and found to contain 93.4% MMA, with an overall recovery of MMA and an MMA yield of 60% and 52% respectively. The condensate was also analyzed by GCMS and found to contain minor impurities of: ethenyl methacrylate; dimethylpentenoate; butyl methacrylate; methylenebutanedioate; Dimethyl 2-methylpentanedioate; (methylpropenyl) propanedioate and dimethyl-1,4-cyclohexane dicarboxylate.

Example 1 (ΊΊ

Decomposition of high impact poly (methyl methacrylate) in the non-resonant cavity

A sample of high impact poly (methacrylate) particles (480 g) was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6), with 0.5 kW of energy supplied for 90 minutes. The reaction temperature recorded during the depolymerization was in the range of 300 ° C to 415 ° C. A sample of the gas from the front layer was removed after 17 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain: carbon dioxide; 2-methyl-1-propene; acrylate; MMA and methyl-2-methyl propanoate. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 85%. The condensate was analyzed by GC and found to contain 71.7% MMA, with an overall recovery of MMA and an MMA yield of 47% and 40% respectively. The condensate was also analyzed by GCMS and found to contain minor impurities of: ethyl methacrylate; styrene; butyl acrylate; dimethylpentenoate and butyl methacrylate.

84 596 ΕΡ Ο 915 917 / ΡΤ 23

Example Ukl

Decomposition of poly (methyl methacrylate) into filings in a mono-mode cavity (laboratory scale)

A sample of poly (methyl methacrylate) chips ("sawdust") (2.1 g), mixed with approximately 1% (w / w) charcoal powder (as microwave susceptor), was irradiated in a microwave cavity mode (Figure 1), with 1 kW of power supplied for 2 minutes. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 98%. The gaseous product was analyzed by GCMS and found to contain predominantly MMA, with traces of styrene, naphthalene and dibutyl phthalate.

Example 1)

Decomposition of poly (methyl methacrylate) gel, in a mono-mode cavity (laboratory scale)

A sample of poly (methyl methacrylate) gel (MMA partially polymerized in the factory) (0.8 g), mixed with approximately 1% (w / w) charcoal powder (as microwave susceptor) was irradiated into a well microwave mode (Figure 1), with 1 kW of power supplied for 2.5 minutes. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 84%. The gaseous product was analyzed by GCMS and found to contain predominantly MMA, with traces of xylene, styrene, 2-methylpropanenitrile and methyl 2-methylbutanoate.

Example 2 - Application of the process of the invention to physical mixtures of polymers

Examples 2 (a) (1)

Decomposition of a physical mixture of polymers, wherein both polymeric substances decompose into their corresponding monomers

A sample of particulate molded transparent poly (meth) acrylate (231 g) and transparent polystyrene pellets (231 g) was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6) with 1 kW of power supplied for 60 minutes. The reaction temperature recorded during the depolymerization was in the range of 330 ° C to 400 ° C. A sample of the gas from the front layer was removed after 22 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain: MMA, 2-methyl-1-propene; carbon dioxide and traces of 2-methylpropanoate of

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Methyl; toluene and styrene. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 70%. The condensate was analyzed by NMR and found to contain 29% (m / m) MMA and 64% (m / m) styrene, with a yield of MMA and styrene of 31% and 67%, respectively. The condensate was also analyzed by GCMS and found to contain impurities in minor amounts of: methyl styrene, styrene dimers and trimers, as well as traces of toluene.

Example 2 (si) (2)

The condensate produced as described in Example 2 (a) (1) and containing 29% (m / m) of MMA and 64% (m / m) of styrene was distilled under vacuum at 60-70 kPa. During distillation, the temperature was incrementally increased from 25 to 150 ° C for approximately 6 hours. The first fraction collected was analyzed by NMR and found to contain 84% (m / m) MMA and 6% (m / m) styrene. The final fraction, also analyzed by NMR, was found to contain 72% (m / m) styrene and 18% (m / m) MMA. Optimization of the distillation procedure will improve the separation of the monomers.

Examples 2 fb &quot;

Decomposition of a physical mixture of polymers, in which both polymeric substances decompose, but only one in its corresponding monomer

A mixture of transparent particulate molded poly (meth) acrylate (209 g) and clear polyethylene beads (209 g) was irradiated in the multiresistant nonresonant microwave cavity (Figure 6), with 1 kW of energy supplied for 45 minutes. The reaction temperature recorded during the depolymerization was in the range of 300 ° C to 390 ° C. A sample of the top gas was withdrawn after 25 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain predominantly MMA, 2-methyl-1-propene and carbon dioxide. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 38%. The condensate was analyzed by GC and found to contain 97.6% MMA. The condensate was also analyzed by GCMS and found to contain impurities in minor amounts of 2-methylbutanoate ester, pentane and hexane esters, styrene, styrene dimer, and C4H2g and C164-32-

Example 2 (c)

Selective decomposition of a physical mixture of polymers, wherein the temperature of 25 84 596

Decomposition and the dielectric loss factors are significantly different

A sample of particulate molded clear poly (meth) acrylate (243 g) and powdered polytetrafluoroethylene (243 g) was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6) with 1 kW of energy supplied during 40 minutes. The reaction temperature recorded during the depolymerization was in the range of 300 ° C to 390 ° C. A sample of the gas from the front layer was removed after 15 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain MMA, 2-methyl-1-propene and carbon dioxide. The mass of the residue in the cavity after irradiation ceased was determined and the loss of mass of the polymer was calculated as 36%. The condensate was analyzed by GC and found to contain 98.6% MMA.

Example 3 - Application of the process of the invention to polystyrene (PS)

Example 3 (a.)

Decomposition of polystyrene in the mono-mode cavity (laboratory scale)

A sample of polystyrene (± 0.5 g) and charcoal (20% by mass) was irradiated in a mono-mode microwave cavity (Figure 1), with 1 kW of energy supplied for 60 seconds. Styrene monomer was recovered from the gases produced. (The supplied and reflected energy and the reaction time were not optimized).

Example 3 tbl

Decomposition of polystyrene in a non-resonant cavity

A sample of transparent polystyrene pellets (481 g) and 10% (w / w) of carbon pellets was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6), with 0.5 kW of energy supplied for 10 minutes. The reaction temperature recorded during the depolymerization was in the range of 200 ° C to 290 ° C. A sample of the top gas was withdrawn after 24 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain styrene, carbon dioxide, benzene, ethylbenzene and toluene. The mass of the residue in the well after the irradiation had ceased was determined and the loss of mass of the polymer was calculated to be 21%. The condensate was analyzed by NMR and found to contain about 60% (w / w) styrene, 30% (w / w) styrene trimer and dimer, 6% (w / w) ethylbenzene and 4% m / m) of toluene. The condensate was also analyzed by GCMS and found to contain small amounts of (1-methylethyl) benzene; (1-methylethenyl) benzene; and benzene. 84 596 ΕΡ Ο 915 917 / ΡΤ 26

The latter compounds were not detected by NMR, since the signals of these compounds were masked by the signals of other compounds present in larger amounts.

Example 4 - Application of the process of the invention to polyethylene terephthalate (PET)

Example 4 (a)

Decomposition of poly (ethylene terephthalate) into the mono-mode cavity

A sample of poly (ethylene terephthalate) (2.01 g) mixed with 0.09 g of charcoal (as microwave susceptor, 4.36% m / m) was irradiated in a mono mode cavity using a power supplied from 1 kW and a total irradiation time of 5 minutes (neither the energy nor the irradiation time were optimized). A mass loss of 66.7% was recorded. The gaseous product was analyzed and found to contain carbon dioxide, acetaldehyde and benzene as major products. The residue was found to contain predominantly terephthalic acid, one of the valuable monomers in the manufacture of PET. With a small amount of unreacted PET.

Example 4 (b)

Decomposition of poly (ethylene terephthalate) in a non-resonant cavity

A sample of transparent polyethylene terephthalate (PET) pellets (717 g) and 10% (m / m) of carbon pellets was irradiated in the multi-purpose non-resonant microwave cavity (Figure 6), with 0.5 kW of power supplied for 30 minutes. The reaction temperature recorded during the depolymerization was in the range of 400 ° C to 470 ° C. A sample of the top gas was withdrawn after 12 minutes of continuous microwave radiation. The gaseous product was analyzed by GCMS and found to contain predominantly carbon dioxide and acetaldehyde. Minor amounts of benzene, ethylbenzene, toluene and styrene were also found in the gas sample. As expected, no condensate was formed in this experiment. The solid product deposited on the walls of the well (outside the reaction zone) was analyzed by NMR and found to contain approximately 44% (w / w) terephthalic acid and 56% (w / w) hydroxy (vinyloxycarbonyl) benzoic acid.

Example 5 - Illustration of polymers that do not degrade into monomers

Example 5

Decomposition of polyethylene in a single-mode cavity (laboratory scale)

A sample of polyethylene (2.4 g) mixed with approximately 14% (w / w) of

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(As microwave susceptor) was irradiated in a mono-mode microwave cavity (Figure 1) using a supplied energy of 2 kW for 2 minutes. The gaseous product was analyzed by GCMS and found to contain propene, hexene, benzene, heptene, as major products and octene, nonene, styrene, 1-propylbenzene, and hydrocarbons having 10 to 23 carbon atoms, as minor products.

Example 5 fbf

Decomposition of polypropylene into a mono-mode cavity (laboratory scale)

A sample of polypropylene (1.5 g) mixed with approximately 15% (w / w) charcoal powder (as microwave susceptor) was irradiated in a mono-mode microwave cavity (Figure 1) using an energy supplied from 1 kW for 20 seconds. The gaseous product was analyzed by GCMS and found to contain propene, hexene, benzene and nonene as the major products, toluene and styrene as minor products, and traces of 1-propynylbenzene, 2-dodecene, naphthalene, C 15 H 30, C 16 H 32, C 12 H 10 , C 14 H 10 and C 16 H 10 O. The process of the invention has several advantages over known processes for the decomposition of the polymers. Advantages of the process of the invention include purity of the product, potential elimination of the need for downstream processing steps, minimal environmental impact, increased energy efficiency due to direct volumetric heating of the polymer, improved occupational health and safety characteristics, and reduced accumulation of solid waste. Improved energy efficiency and reduced volumes of effluents (such as washing effluent and lead residue in the case of PMMA) provide significant advantages of operating costs of the microwave process over alternative and more conventional depolymerization processes, despite a higher initial investment cost.

In particular, the invention provides a process which is of particular use for poly (methyl methacrylate) as a polymeric species. On the basis of extensive bench scale studies (1.5-2 kg / h) for PMMA, a comparison of production costs (variables, excluding the cost of PMMA waste, and fixed operating costs, excluding depreciation) for microwaves and lead bath processes show gains of 74% for the microwave process over the lead bath. This is due to the fact that energy costs can be reduced up to 61%, while the cost of the chemicals can be reduced by 87%, eliminating downstream processing steps (e.g. washes). In addition, the disposal of solid and aqueous effluents considerably reduces the cost of effluent treatment and environmental control by up to 94%. 28 84 596

ΕΡ Ο 915 917 / EN

Including the cost of the PMMA residue, this translates to 11% gains in the cost of production for the microwave process, compared to the lead bath process.

Lisbon,

19. Mftl 2DOO

By AECI LIMITED - THE OFFICIAL AGENT -

CUNHA FERREIRA Ag. Of. Pr. Ind. Duo das Flores, 74 - 4 ° 1 SOO LISBOA I

Claims (10)

A process for the decomposition of a polymer which is capable of undergoing thermal depolymerization for its monomer or monomers, the polymer being selected from the group consisting of poly (methyl methacrylate), polytetrafluoroethylene, polystyrene, poly (ethylene terephthalate), poly (α-methylstyrene) and polyisobutylene, and to recover at least one of the monomers, which comprises the steps of: (i) subjecting the polymer in a solid, gel form, partially molten or fused to a heating with microwaves for a period of time and at a temperature sufficient to decompose the polymer to produce the monomer or monomers in a gaseous, liquid or solid form without substantial decomposition of the monomer or monomers; and (ii) recovering at least one of the monomers or monomer. A process as claimed in claim 1, wherein the process comprises the step of: (iii) when two or more monomers are recovered in step (ii), separation of the monomers from one another; A process as claimed in claim 1 or claim 2, wherein the process comprises the steps of: (iv) when the monomer or monomers are in the gaseous form, condensation of the monomer or monomers. A process according to any one of claims 1 to 3, wherein the process comprises the step of: (v) purifying the condensed monomer or monomers. A process according to any one of claims 1 to 4, wherein before step (i) the polymer is preheated to a suitable temperature. A process according to any one of claims 1 to 5, wherein in step (i) the polymer is mixed with a microwave absorber or susceptibiliser. 84 596 ΕΡΟ915 917 / EN 2/2 A method according to any one of claims 1 to 6, wherein step (i) is carried out under an inert atmosphere. A process as claimed in any one of claims 1 to 7, wherein in step (i) the microwave heating is effected in a well of a mono-mode, multi-mode or non-resonant microwave reactor. A process according to any one of claims 1 to 8, wherein the polymer is selected from the group consisting of poly (methyl methacrylate), polytetrafluoroethylene, poly (α-methylstyrene), polystyrene and polyisobutylene. A process according to claim 9, wherein the polymer is poly (methyl methacrylate). Lisbon, 19. MAI 2D0u By AECI LIMITED - THE OFFICIAL AGENT - Ag. Of. Pr. Ind. J Rua des Flores, 74 - - 1SGO LISBO / i DA CUNHA FERRi: